To add one more thing that I haven't noticed in the other discussions on this board: Has anyone seen the IQ tests in Africa?
I used to do a little community work in Namibia (so I can't speak for any of the other countries), and I know that the IQ tests in this country were administered in English. From my experience with the locals, they all had decent English (for most of them, English was either a second or third or fourth or fifth language!!), but it was nothing that would have allowed them to ace some standardized test. Asking a Namibian to take an IQ test in English would be equivalent to asking some American kid who had taken two years of Spanish in high school to take his IQ test in Spanish. I doubt he would have had a very high IQ score.
Now if the Namibians had someone give them IQ tests in one of their 14+ native languages, I bet the average would come out on par with any other racial group's. Of course, since it's virtually impossible to develop an IQ test for a language that only had a writing system developed in the last 20 years or so, I doubt that's going to happen.
In my time in Namibia, I met exactly zero people who spoke only one language. In America, I don't even keep count.